ON THE DEVELOPMENT OF PARASITIC COPEPODS. 55 



artefacts, and that the differentiation shown by many stains is due 

 to differences in the size and density of particles of protoplasm 

 coagulated by fixation as claimed by some writers. I have paid 

 special attention to the structure of coagulated proteids, and 

 repeated experiments of Fischer and others by producing granu- 

 lar and " curdled " precipitates, and aster-like formations in albu- 

 min, and by staining the same. These led me to believe that 

 probably none of the finest structures seen in the fixed proto- 

 plasm could be relied upon as representing structures in the living 

 cell, but that such large bodies as chromosomes, spheres, etc., 

 could not be considered artefacts, though their finer structure 

 may be changed. 



In the cell lineage I have used the quartet system of nomen- 

 clature (of Kofoid, '94) as applied by Bigelow to Lepas (the only 

 crustacean whose cell lineage has been described beyond the 16 

 cell stage) to facilitate comparison among Crustacea, but do not 

 think this type of cleavage closely related to that of annelids and 

 molluscs, in fact the cleavage of the parasitic copepods does not 

 follow a quartet system and I hope no one will be misled by the 

 inappropriate nomenclature. 



The cells of the 4 cell stage are designated a, b, c, d in a 

 dextral order, a being the left anterior cell. An exponent 

 denotes the order of the generation starting with the ovum as 

 the first. A second exponent is used to distinguish a cell from 

 other cells of the same generation and derivation. The odd 

 numbers refer in cases of equatorial division to cells nearer the 

 vegetal pole ; of transverse, to cells nearer the anterior end ; of 

 longitudinal, to cells nearer the sagittal plane, or in case the 

 cleavage coincides with that plane, the right side. Thus equa- 

 torial refers to the equator of the chief axis of the egg while sagit- 

 tal and transverse to the axes of the embryo that will develop 

 therefrom, but which may be distinguished in the egg as early 

 as the 2 cell stage. 



To determine the second exponent of the two daughter cells 

 of any cell division, multiply the second exponent of the mother 

 cell by two and the product is the second exponent of that 

 daughter cell which has an even number for this exponent, and is 

 one greater than the second exponent of the daughter cell which 

 has an odd number for a second exponent. 



